Effects Of Afforestation And Thinning On Greenhouse Gas Emissions From Temperate Abandoned-land Soil In The Northeast Of China

This paper studied the effects of different selective cutting intensity（no cutting,mild selective cutting-25%and severe selective cutting-50%,and these sites were established for 20years）on the CO₂,CH₄ and N₂O emission fluxes from Larch plantations（50-year old）on abandoned-land by using static chamber and gas chromatography methods,and the air temperature,soil temperature and soil moisture were measured simultaneously in the Maoershan region,Northeast China.The purpose of this study was to evaluate the effect and influencing mechanism of different selective cutting intensity on maoershan Larch plantations greenhouse gas flux seasonal pattern,main control factor and global warming potential.carbon source or sink.The result shown that:（1）Annual soil temperature at the 0⁴0 cm depth in no cutting site,mild selective cutting site and severe selective cutting site of Larch plantations were decreased significantly than farmland site,decreased by 0.47².56°C、0.79³.03°C、0.96³.88°C respectively.The soil moisture in the depth of 15⁴0 cm and 5⁴0cm in the no cutting and mild selective cutting by1.6%⁵.0%and 2.0%⁴.0%significantly.However,the soil moisture in the depth of 0⁴0 cm in the severe selective cutting by 3.7%⁹.9%significantly.（2）Annual mean emission fluxes of CO₂ ranged from 149.44 to 204.82 mg·m^-2·h^-1,took on the trends of no cutting site>farmland site>mild selective cutting site（25%）>severe selective cutting site（50%）,which increased by 11.6%at no cutting site,yet that reduced by11.4%¹8.6%at mild and severe selective sites compared with farmland site,and both significantly reduced by 20.6%and 27.0%compared with no cutting site.So CO₂ flux（heterotrophic respiration）in the 50-year old Larch plantations was higher than farmland sites.And soil CO₂ flux was lower than farmland sites after selective cutting management,lower than no cutting sites significantly.Larch plantations and different selective cutting intensity sites changed the seasonal pattern of soil CO₂ efflux.The pattern of soil CO2 efflux in farmland site and selective cutting site were summer>spring>autumn>winter.The pattern of soil CO₂ efflux in no cutting site and severe selective site were summer>spring≈autumn>winter.（3）Annual absorption fluxes of CH₄ ranged from-0.027 to-0.033 mg·m^-2·h^-1,was in order of severe selective site>no cutting site=farmland site>mild selective site,which decreased by 12.9%at mild selective sites,and increased by 6.5%at severe selective site compared with no cutting site and farmland site.So Larch plantations on abandoned-land and selective cutting management did not affect the absorption fluxes of CH₄.The flux of CH₄ in all sites were absorption in spring,summer and autumn,and emission in winter.There were two seasonal patterns:the absorption of CH₄ in farmland site and severe selective cutting site were summer>spring>autumn;no cutting site and mild selective cutting site were spring≈summer≈autumn,and the emission of CH₄ in no cutting site and mild selective cutting were higher than farmland site and severe selective site.So Larch plantations on abandoned-land and mild selective cutting changed the CH₄ flux seasonal pattern.（4）N₂O emission fluxes ranged from 0.025 to 0.037 mg·m^-2·h^-1,was in order of farmland site>severe site>mild selective site>no cutting site,which reduced by 24.3%³2.4%at three cutting and no cutting sites compared with farmland site,but increased by 4.0%or 12.0%at mild and severe selective sites than no cutting site.Larch plantations and different selective cutting intensity sites changed the seasonal pattern of soil N₂O efflux.The pattern of N₂O emission in farmland was spring≧summer≧autumn≈winter.No cutting site,mild selective cutting site and severe selective cutting site were spring>summer≈autumn≈winter（the last two were absorption）,spring>summer>autumn≈winter and spring>summer≈autumn≈winter.（5）Derelict land afforestation and selective cutting management had no effects on the relationship between greenhouse gas emission and soil temperature,but the relationship with soil moisture were changed.（6）The global warming potential（GWP）was in order of derelict land afforestation site>farmland site>mild selective site>severe selective site.The GWP increased by 9.1%at no cutting site,but decreased by 12.1%and 18.7%at mild and severe selective cutting sites respectively,compared with farmland site,and also both decreased by 19.4%and 25.5%than no cutting site.Therefore,derelict land Larch plantation increased soil GWP in Northeast China.And selective cutting management decreased soil GWP in a big degree.So moderate intensity selective cutting（25%⁵0%）in Larch plantation was the better way to reduce greenhouse gas emissions.